§ 340.170. Driving To The Right.

A. 

Upon all public roads or highways of sufficient width, a vehicle shall be driven upon the right-half of the roadway, except as follows:

1. 

When overtaking and passing another vehicle proceeding in the same direction pursuant to the rules governing such movement;

2. 

When placing a vehicle in position for and when such vehicle is lawfully making a left turn in compliance with the provisions of this Title;

3. 

When the right-half of a roadway is closed to traffic while under construction or repair; or

4. 

Upon a roadway designated by local ordinance as a one-way street and marked or signed for one-way traffic.

B. 

It is unlawful to drive any vehicle upon any highway or road which has been divided into two (2) or more roadways by means of a physical barrier or by means of a dividing section or delineated by curbs, lines or other markings on the roadway except to the right of such barrier or dividing section or to make any left turn or semi-circular or U-turn on any such divided highway, except at an intersection or interchange or at any signed location designated by the State Highways and Transportation Commission or the Department of Transportation. The provisions of this Subsection shall not apply to emergency vehicles, law enforcement vehicles or to vehicles owned by the Commission or the Department.

C. 

Whenever any roadway has been divided into three (3) or more clearly marked lanes for traffic, the following rules in addition to all other consistent herewith shall apply:

1. 

A vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from such lane until the driver has first ascertained that such movement can be made with safety.

2. 

Upon a roadway which is divided into three (3) lanes, a vehicle shall not be driven in the center lane except when overtaking and passing another vehicle where the roadway ahead is clearly visible and such center lane is clear of traffic within a safe distance, or in preparation for a left turn, or where such center lane is at the time allocated exclusively to traffic moving in the direction the vehicle is proceeding and is signposted to give notice of such allocation.

3. 

Upon all highways any vehicle proceeding at less than the normal speed of traffic thereon shall be driven in the right-hand lane for traffic or as close as practicable to the right-hand edge or curb, except as otherwise provided in Sections 304.014 to 304.026, RSMo.

4. 

Official signs may be erected by the State Highways and Transportation Commission or the Highway Patrol may place temporary signs directing slow-moving traffic to use a designated lane or allocating specified lanes to traffic moving in the same direction and drivers of vehicles shall obey the directions of every such sign.

5. 

Drivers of vehicles proceeding in opposite directions shall pass each other to the right and, except when a roadway has been divided into traffic lanes, each driver shall give to the other at least one-half (½) of the main traveled portion of the roadway whenever possible.

D. 

All vehicles in motion upon a highway having two (2) or more lanes of traffic proceeding in the same direction shall be driven in the right-hand lane except when overtaking and passing another vehicle or when preparing to make a proper left turn or when otherwise directed by traffic markings, signs or signals.